WASHINGTON (CNN) -- Republican Sen. John McCain of Arizona broke forcefully with President Bush and the Senate GOP leadership Tuesday evening over the issue of same-sex marriage, taking to the Senate floor to call a constitutional amendment that would effectively ban the practice unnecessary -- and un-Republican.

"The constitutional amendment we're debating today strikes me as antithetical in every way to the core philosophy of Republicans," McCain said. "It usurps from the states a fundamental authority they have always possessed and imposes a federal remedy for a problem that most states do not believe confronts them."

The proposed amendment died Wednesday after a procedural vote to move the measure to the Senate floor failed 48-50, or 12 votes short of the 60 required by Senate rules. (Full story)

McCain said Tuesday night he would side with opponents of the amendment on the procedural vote to make clear to his constituents that he is against the amendment itself.

McCain also said the amendment "will not be adopted by Congress this year, nor next year, nor any time soon until a substantial majority of Americans are persuaded that such a consequential action is as vitally important and necessary as the proponents feel it is today."

"The founders wisely made certain that the Constitution is difficult to amend and, as a practical political matter, can't be done without overwhelming public approval. And thank God for that," he said.

A constitutional amendment needs a two-thirds majority of both houses of Congress to pass. Then the proposal would need the approval of three-fourths of the state legislatures to be ratified.

Bush, who defeated McCain for the Republican presidential nomination in 2000, has championed the amendment, saying it is necessary to defend the institution of marriage from "activist judges."

Social conservatives have been pushing hard for the measure since May, when Massachusetts' highest court legalized same-sex marriages in the Bay State.

But McCain argued on the Senate floor that there are "far less draconian" remedies, including the 1996 Defense of Marriage Act -- which defined marriage for purposes of federal law as a union between a man and a woman and allowed states to refuse to recognize same-sex marriages legally performed in other states -- and state constitutional amendments limiting marriage to heterosexual couples.

He said if the U.S. Supreme Court strikes down the Defense of Marriage Act or "state remedies to judicial activism fail," then amending the federal Constitution might be "appropriate."

But he said the decision in Massachusetts to legalize same-sex marriages does "not represent a death knell to marriage."

"What evidence do we have that states are incapable of further exercising an authority they have exercised successfully for over 200 years?" McCain said.

"We will have to wait a little longer to see if Armageddon has arrived."